Mature B-cell leukemias with more than 55% prolymphocytes: report of 2 cases with Burkitt lymphoma-type chromosomal translocations involving c-myc.

CONTEXT: The molecular genetic events involved in the pathogenesis of mature B-cell leukemias with more than 55% prolymphocytes are not well characterized. We have encountered 2 such cases in which conventional cytogenetic analysis identified Burkitt lymphoma-type chromosomal translocations involving 8q24.

OBJECTIVE: To assess these 2 cases for involvement of the c-myc gene using fluorescence in situ hybridization analysis with probes specific for the c-myc and immunoglobulin heavy-chain (IgH) genes.

RESULTS: In both cases, conventional cytogenetic analysis demonstrated complex karyotypes, including chromosomal translocations involving 8q24. In case 1, a case of de novo prolymphocytic leukemia, the t(8;14)(q24;q32) was detected. In case 2, a case of chronic lymphocytic leukemia in prolymphocytoid transformation, the t(8;22)(q24;q11) was identified. Fluorescence in situ hybridization studies showed c-myc/IgH fusion signals in case 1, proving the presence of the t(8;14). Split c-myc signals without fusion to IgH were observed in case 2, proving c-myc gene rearrangement and consistent with the t(8;22).

CONCLUSION: These results suggest that c-myc gene alterations may be involved in the pathogenesis of a subset of mature B-cell leukemias with more than 55% prolymphocytes.